代幣的每日 DEX OHLC 與 VWAP，使用精確分數

interface DexDailyPrice {
  first_price_numerator: string;
  first_price_denominator: string;
  last_price_numerator: string;
  last_price_denominator: string;
}

// 1. 不經浮點數轉換的比率比較：檢查收盤價是否高於開盤價
// a / b > c / d  等價於  a * d > c * b
export function isPriceUp(row: DexDailyPrice): boolean {
  const openNum = BigInt(row.first_price_numerator);
  const openDen = BigInt(row.first_price_denominator);
  const closeNum = BigInt(row.last_price_numerator);
  const closeDen = BigInt(row.last_price_denominator);

  return closeNum * openDen > openNum * closeDen;
}

// 2. 將分數轉換為指定小數位數的定點十進位字串（不損失浮點精確度）
export function fractionToFixedString(
  numeratorStr: string,
  denominatorStr: string,
  decimals = 18
): string {
  const num = BigInt(numeratorStr);
  const den = BigInt(denominatorStr);
  if (decimals === 0) {
    return (num / den).toString();
  }
  const scaleFactor = 10n ** BigInt(decimals);

  const scaled = (num * scaleFactor) / den;
  const intPart = scaled / scaleFactor;
  const remainder = scaled % scaleFactor;
  const fracPart = remainder.toString().padStart(decimals, "0");

  return `${intPart}.${fracPart}`;
}

from decimal import Decimal, getcontext
from fractions import Fraction

# 1. 使用 fractions.Fraction 進行精確有理數計算
open_price = Fraction(
    int(row["first_price_numerator"]),
    int(row["first_price_denominator"])
)
close_price = Fraction(
    int(row["last_price_numerator"]),
    int(row["last_price_denominator"])
)

# 不經浮點數四捨五入誤差的精確價格變動
price_delta = close_price - open_price
print(f"Price delta (fraction): {price_delta}")

if open_price != 0:
    percentage_change = (price_delta / open_price) * 100
    print(f"Percentage change: {float(percentage_change):.4f}%")

# 2. 使用 decimal.Decimal 進行任意精確度的小數運算
getcontext().prec = 50

if int(row["first_price_denominator"]) != 0:
    open_decimal = Decimal(row["first_price_numerator"]) / Decimal(row["first_price_denominator"])
    print(f"High-precision open: {open_decimal}")

interface DateSpan {
  from: string;
  to: string;
}

/**
 * 將大型日期範圍切分為最多 maxDays（預設：90）天的連續區間
 */
export function splitDateRange(startDateStr: string, endDateStr: string, maxDays = 90): DateSpan[] {
  const spans: DateSpan[] = [];
  let currentStart = new Date(startDateStr);
  const end = new Date(endDateStr);

  while (currentStart <= end) {
    const chunkEnd = new Date(currentStart);
    chunkEnd.setUTCDate(chunkEnd.getUTCDate() + (maxDays - 1));
    const effectiveEnd = chunkEnd < end ? chunkEnd : end;

    spans.push({
      from: currentStart.toISOString().slice(0, 10),
      to: effectiveEnd.toISOString().slice(0, 10),
    });

    const nextStart = new Date(effectiveEnd);
    nextStart.setUTCDate(nextStart.getUTCDate() + 1);
    currentStart = nextStart;
  }

  return spans;
}

/**
 * 跨多個 90 天分段回填代幣每日價格
 */
export async function backfillTokenDailyPrices(
  chain: string,
  token: string,
  startDate: string,
  endDate: string,
  apiKey: string
) {
  const chunks = splitDateRange(startDate, endDate, 90);
  const allDailyPrices = [];

  for (const chunk of chunks) {
    const url = new URL(`https://api.blockvectra.com/v1/data/${chain}/dex/prices`);
    url.searchParams.set("token", token);
    url.searchParams.set("from", chunk.from);
    url.searchParams.set("to", chunk.to);

    const res = await fetch(url, {
      headers: { "x-api-key": apiKey },
    });

    if (!res.ok) {
      throw new Error(`Failed to fetch span ${chunk.from}..${chunk.to}: HTTP ${res.status}`);
    }

    const json = await res.json();
    allDailyPrices.push(...json.data);
  }

  return allDailyPrices;
}